1. Field of the Invention
The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device that has organic light emitting diodes stacked in a double layer. The present invention also relates to a method of fabricating the organic light emitting display device.
2. Description of the Related Art
FIG. 1 is a circuit diagram of a unit pixel of a conventional organic light emitting display device. Referring to FIG. 1, a scan line S, a data line D, and a common power line ELVDD are disposed. A unit pixel is defined by an intersection of the data line D and the scan line S.
The unit pixel includes an organic light emitting diode (OLED), which has an anode, a cathode, and an organic emission layer formed between the anode and the cathode. The unit pixel also includes a switching transistor Ma, a capacitor Cst, and a driver transistor Mb. The switching transistor Ma has a gate connected to the scan line S and a source connected to the data line D. The switching transistor Ma switches a data signal applied to the data line by a scan signal applied to the scan line S. The capacitor Cst is connected between the common power line ELVDD and the drain of the switching transistor Ma, and maintains the data signal for a predetermined time. The driver thin film transistor Mb has a gate connected to the capacitor Cst, a source connected to the common power line ELVDD, and a drain connected to the anode of the OLED. The driver thin film transistor Mb supplies a current proportional to the magnitude of the data signal to the anode. A cathode voltage ELVSS, having a level lower than the power supply voltage applied to the common power line, is applied to the cathode of the OLED. As a result, holes from the anode and electrons from the cathode are injected into the organic emission layer. The injected holes and electrons are combined in the organic emission layer to create excitons, which emit light by transitioning from an excited state to a ground state.
FIGS. 2A and 2B [These figures are too dark—please send copies with better contrast] are photographs illustrating short failures between an anode and a cathode of an OLED. To detail this, FIG. 2A shows a short failure between the anode and the cathode caused by a foreign substance. FIG. 2B shows a short failure between the cathode and the anode due to the cathode being pressed by an external impact.
When a short failure occurs between the anode and the cathode due to errors in the manufacturing process, the OLED no longer emits light. Consequently, the unit pixel having the OLED where the short failure has occurred becomes a dark pixel, which lowers the yield of displays that meet commercial specifications.